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	The CoreTidy/CorePrep/CoreToStg saga continues
	[actually, this commit mostly completes the job]
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			DO NOT MERGE!

* CorePrep injects implicit bindings, not the type checker,
  nor CgConTbls.   (This way, all the code generators see
  them, so no need to fiddle with the byte code generator.)

  As a result, all bindings in the module are for LocalIds,
  at least until CoreTidy.   This is a Big Win.

  Hence remove nasty isImplicitId test in update_bndr in
  SimplCore and DmdAnal

* hasNoBinding is no longer true of a dataConId (worker).
  There's an implicit curried binding for it.

* Remove yukky test in exprIsTrivial that did not regard
  a hasNoBinding Id as trivial; similarly in SimplUtils.tryEtaReduce

* In CoreTidy, get the names to avoid from the type env.
  That way it includes implicit bindings too.

* CoreTidy set the Arity of a top-level Id permanently;
  it's up to the rest of the compiler to respect it.
  Notably, CorePrep uses etaExpand to make the manifest arity
  match the claimed arity.

* As a result, nuke CgArity, so that CgInfo now contains only
  CafInfo.  The CafInfo is knot-tied as before.


Other things

* In Simplify.simplLazyBind, be a bit keener to float bindings
  out if it's a top-level binding.